It is known for pressure to be exerted on areas of a human body under examination with probes, such as feelers, stimulators, glass bulbs, of medical appliances, especially tonometers and esthesiometers. This can, for instance, be achieved by weights, weighted levers or other members under spring tension or subject to a collapsing force. The disadvantages of generating pressure in such manner lie in the inherent jolting pressure changes, in its compulsory direction and also in most cases in the patients having to lie down during the examination. With appliances equipped with springs, the distance between them and the patient is often a measure for the applied force; if these appliances are hand-held, an error frequently enters into the measured result caused by unsteady holding. It is also known to evaluate diverse buckling forces which result out of the insertion length of plastic threads. However, this leads to great inaccuracy, since the plastic threads are bent within themselves so that no real buckling forces need to be generated and also by the hygroscopic properties of the thread material.
All known appliances have the common disadvantage that simple and often desired subsequent electrical processing of the measured results is not directly possible.
It is therefore the object of the present invention to create an apparatus for the generation of a defined force and the measurement thereof in medical examination appliances independent of position or travel of transmitting members which avoids the disadvantages described above of the known appliances and which permits electric subsequent processing of the measured results.
In order to achieve this object, an apparatus is proposed for the generation and measurement of defined forces independent of position or travel of transmitting members for medical examination appliances which, according to the invention, embodies a combination of the following features:
(a) In a housing, a two-armed lever pivotably mounted about a horizontal axis for movement in a vertical plane, the center of gravity of the lever coinciding with the pivot axis of the lever, a contact probe for engaging a body area under examination attached to the free end portion of the upper arm of the lever;
(b) a force producing means including a permanent magnet system and a rectangular coil secured to the free end of the lower arm of the lever, the rectangular coil when moving the lever adapted to move, with at least one side portion, through a homogeneous magnetic field generated by the permanent magnet system, narrow strips of gold with a negligibly small resisting torque connecting the rectangular coil with electronic control and measuring circuitry;
(c) the electronic control and measuring circuitry for energizing the coil including a voltage-controlled constant current source connected with a control indicator, an input keyboard for setting the output voltage of the electronic circuitry, maximum and minimum limiters in the form of limit switches operatively coupled to the integrator, and indicating means such as a voltmeter;
(d) the extent of movement of the lever about its pivot axis in the homogeneous field of the permanent magnet system being adapted to being restricted;
(e) the movement of the lever being mechanically controlled by a motor-driven cam plate serving as detent, being connected with a motor control to effect controlled movements of the contact probe;
(f) the heart-shaped cam plate being connected to the motor through an interposed gear train;
(g) within the operational range of the cam plate, a slide being secured to the free end of the lower arm of the lever and a light barrier system for movement control of the lever being disposed.
It is possible with such apparatus in appliances for medical examination to generate and measure defined forces independent of position or travel of transmitting members and, subsequently, to process the measured results electrically. It is not necessary anymore that the patient lies down. Precise measurements are possible in all attitudes of the patient. Measuring errors which are normally caused by unsteady holding of examination equipment are avoided with the appliance according to the invention. A slide at the lower arm of the lever and light barriers controlling the lever movement being disposed within the operational range of the cam plate together achieve the advantage that the body area under examination absorbs the pressure while the cam plate continues to rotate until its widest part masks both light barriers. Then, the lever has its greatest freedom of movement and, when the key is released, the cam plate automatically reverses its rotation and lifts the contact probe off the body area.